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Abstract:

The present invention provides a system for treating carbon dioxide, and a
method by which such treated carbon dioxide can be stored underground at
low cost and with high efficiency. The present invention' method for
storing carbon dioxide underground includes: a step for pumping up to the
ground groundwater from a pumping well in a deep aquifer, and then
producing injection water. Carbon dioxide that has been separated and
recovered from exhaust gas from a plant facility is changed into the
bubbles. The bubbles are mixed with the injection water, and hereby
produces a gas-liquid mixture a step for injecting into. The deep aquifer
is injected into the gas-liquid mixture from the injection well. The
method preferably further includes a step for dissolving a cation-forming
material in the injection water, and a step for injecting the injection
water, in which the cation-forming material is dissolved, into the deep
acquifer at its top and above the place at which injection water has
already been injected.

Claims:

1. A method for storing carbon dioxide underground, comprising:a step for
pumping up groundwater from a deep aquifer through a pumping well to
aboveground, so as to produce injection water;a step for changing carbon
dioxide that has been separated and recovered from exhaust gas from a
plant facility into fine bubbles, and mixing the carbon dioxide bubbles
with said injection water so as to produce a gas-liquid mixture; anda
step for injecting said gas-liquid mixture through an injection well into
the deep aquifer.

2. The method described in claim 1 for storing carbon dioxide underground,
comprising:a step for dissolving a cation-forming material in said
injection water; anda step for injecting said injection water, in which
said cation-forming material is dissolved, into the top portion of said
deep aquifer, at a position higher than where said gas-liquid mixture has
already been injected.

3. A system for storing carbon dioxide underground, comprising:a pumping
well that reaches a deep aquifer;a pump which pumps up groundwater from
said pumping well;an injection well that reaches said deep aquifer;a
liquid injection device that feeds into said injection well as injection
water said groundwater, that has been pumped up;a gas injection device
that feeds into said injection well carbon dioxide that has been
separated and recovered from exhaust gas from a plant facility; anda
nozzle that is arranged inside said injection well and that changes said
carbon dioxide into fine bubbles,wherein said carbon dioxide is changed
into fine bubbles and carbon dioxide bubbles are dissolved in said
injection water, anda gas-liquid mixture, which is a mixture of the fine
bubbles of said carbon dioxide with said injection water, is injected
into said deep aquifer.

4. The system described in claim 3 for storing carbon dioxide underground,
whereina double pipe that includes an outer pipe and an inner pipe is
installed in said injection well,said injection water is fed into between
said outer pipe and said inner pipe, andsaid carbon dioxide is fed into
said inner pipe.

5. The system described in claim 4 for storing carbon dioxide underground,
whereinsaid nozzle has an outside diameter equal to the inside diameter
of said outer pipe, and said nozzle is mounted to the top end of said
inner pipe,wherein said nozzle includesan injection-water spray pipe
formed inside said nozzle, and one end of which is open at the top of
said nozzle between said outer pipe and said inner pipe, and the other
end of which is open at the bottom of said nozzle, anda carbon-dioxide
spray pipe, one end of which is open at said inner pipe at the top of
said nozzle, and the other end of which is connected to an intermediate
part of said injection-water spray pipe.

6. The system described in claim 5 for storing carbon dioxide underground,
further comprising:a device for raising and lowering said inner pipe;
anda cation-forming-material dissolving device;wherein said inner pipe
and said nozzle, which have been installed so as to reach said deep
aquifer, are pulled up to the top of said deep aquifer, andthe injection
water, in which the cation-forming material is dissolved, is injected
into a position higher than where said gas-liquid mixture has already
been injected.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]The present Application is based on International Application No.
PCT/JP2007/062915, filed on Jun. 27, 2007, which in turn corresponds to
Japanese Application No. 2006-178345 filed on Jun. 28, 2006, and priority
is hereby claimed under 35 USC § 119 based on these applications.
Each of these applications are hereby incorporated by reference in their
entirety into the present application.

FIELD OF THE INVENTION

[0002]The present invention relates to the storing underground of carbon
dioxide (CO2) that is in exhaust gas generated from a combustion
furnace or an incinerator, and more particularly to a method and system
for treating carbon dioxide without the need for a facility that changes
carbon dioxide into a supercritical fluid.

BACKGROUND OF THE INVENTION

[0003]As a countermeasure against global warming, it is Japan's duty to
reduce, between 2008 and 2012, the emission volume of greenhouse gas by
an average of 6% per annum from the level of 1990. However, in 2002, the
volume of Japan's greenhouse-gas emissions increased by 7.6% over the
volume for 1990. If this continues, it will be difficult to achieve the
6% reduction goal. Therefore, the government has adopted the Kyoto
Protocol Target Achievement Plan, which has standards stricter than those
of existing countermeasures against global warming, and which presents
goals for reducing the CO2 that is emitted when energy is utilized
in various sectors of societal activity. The plan provides that, for 2010
the volume of CO2 emissions from the energy-conversion sector (e.g.,
power plants) should be 16.1% less than in 1990, the volume from the
industrial sector should be 8.6% less, the volume from the transportation
sector should not be more than 15.1% higher, the volume from the other
sector including the service sector should not be more than 15.0% higher,
and the volume of household emissions should not be more than 6.0%
higher. However, in Japan, energy-saving measures have already been
implemented in the industrial sector, where the largest reduction in
CO2 emission volume can be expected. Therefore, the cost of further
reducing carbon dioxide emissions will be significantly high, which is a
problem.

[0004]Greenhouse gas includes six kinds of gases, e.g., carbon dioxide,
methane, and hydrochlorofluorocarbon. In Japan, however, 90% or more of
the greenhouse gas that is emitted is carbon dioxide. The United States
and the European Union are storing carbon dioxide underground as an
effective measure for reducing that greenhouse gas, but in Japan, storing
carbon dioxide underground is considered unsuitable due to Japan's
geological conditions as well as the frequent earthquakes that occur in
this country. The conventional method of storing carbon dioxide
underground is to seal carbon dioxide, which is in the form of a
supercritical fluid (i.e., under high temperature and high pressure,
where a distinction between liquid and gas cannot be made), under a rigid
sealing layer or caprock layer. However, in Japan it is difficult to find
a place that is economical and suitable for that type of storage. Patent
Document 1, "Method for Operating a System of Separation and Recovery of
Carbon Dioxide By Using a Steel Plant Facility," discloses a system for
separating and recovering carbon dioxide from byproduct gases emitted
from a steel plant. The carbon dioxide that is separated and recovered
from the steel plant is fed to an immobilizing facility via a
transportation means such as a pipe. The carbon dioxide in the
immobilizing facility is then injected into an aquifer underground,
injected into a depleted gas field, or stored in the ocean, so that the
carbon dioxide is immobilized. Patent Document 2, "Device for
Liquefaction and Sedimentation of Gases," discloses that seawater and
carbon dioxide that has been liquefied under high pressure are
alternately pumped and fed deep into the sea. [0005]Patent Document 1:
Japanese Patent Application Publication No. 2004-237167 [0006]Patent
Document 2: Japanese Patent Application Publication No. 2000-227085

SUMMARY OF THE INVENTION

[0007]The objectives of the present invention are to provide (1) a method
by which carbon dioxide can be stored underground at low cost and with
high efficiency, and (2) a system for treating carbon dioxide to enable
its use with that method.

[0008]In one aspect of the invention, the present invention describes a
method for storing carbon dioxide underground.

[0009]The method includes a step for pumping up groundwater from a deep
aquifer through a pumping well to aboveground, so as to produce injection
water. Carbon dioxide that has been separated and recovered from the
exhaust gas from a plant facility is changed into fine bubbles, and the
carbon dioxide bubbles are mixed with the injection water so as to
produce a gas-liquid mixture. The gas-liquid mixture is injected through
an injection well into the deep aquifer.

[0010]In another aspect of the present invention, cation-forming material
is dissolved in said the injection water. The injection water is
injected, in which the cation-forming material has been dissolved, into
the top portion of the deep aquifer, at a position higher than where the
gas-liquid mixture has already been injected.

[0011]In yet another aspect of the present invention a system is disclosed
for storing carbon dioxide underground, with the system including a
pumping well that reaches a deep aquifer, a pump that pumps up
groundwater from the pumping well, an injection well that reaches the
deep aquifer, a liquid injection device that feeds into the injection
well as injection water the groundwater that has been pumped up, a gas
injection device that feeds into the injection well carbon dioxide that
has been separated and recovered from exhaust gas from a plant facility,
and a nozzle that is arranged inside the injection well and that changes
the carbon dioxide into fine bubbles.

[0012]The carbon dioxide bubbles are dissolved in the injection water, and
the gas-liquid mixture, which is a mixture of the fine bubbles of the
carbon dioxide and the injection water, is injected into the deep
aquifer.

[0013]In a still further aspect of the present invention, a double pipe
includes an outer pipe and an inner pipe is installed in the injection
well. The injection water is fed into between the outer pipe and the
inner pipe, and the carbon dioxide is fed into the inner pipe.

[0014]In yet another aspect of the present invention, the nozzle has an
outside diameter equal to the inside diameter of the outer pipe. The
nozzle is mounted to the top end of the inner pipe. An injection-water
spray pipe that is at the top of the nozzle, and one end of which is open
between the outer pipe and the inner pipe, and the other end of which is
open at the bottom of the nozzle. A carbon-dioxide spray pipe is at, one
end of which is open at the inner pipe at the top of the nozzle, and the
other end of which is connected to an intermediate part of the
injection-water spray pipe.

[0015]In yet another aspect of the present invention a device raises and
lowers the inner pipe, and a cation-forming-material dissolving device
the inner pipe and the nozzle, which have been installed so as to reach
the deep aquifer, are pulled up to the top of the deep aquifer. The
injection water, in which the cation-forming material is dissolved, is
injected at a place higher than where the gas-liquid mixture has already
been injected.

[0016]The method of the present invention for storing carbon dioxide
underground has the following effect. When carbon dioxide--in the form of
fine bubbles or as a supercritical fluid--is dissolved into groundwater
that has been pumped up from a deep aquifer, about 50 kg of carbon
dioxide becomes dissolved in 1 m3 (1000 kg by weight) of water,
under high pressure and at a high temperature in the deep aquifer. Carbon
dioxide in the form of fine bubbles can be diffused more widely in a deep
aquifer than can a supercritical fluid that becomes solidified (becomes a
plume) after being injected into a deep aquifer. In addition, the area of
contact between groundwater and carbon dioxide in the form of fine
bubbles is significantly larger than the area of contact between
groundwater and a supercritical fluid. Therefore, the rate of solution of
the carbon dioxide in the form of fine bubbles into groundwater is
several hundred to several thousand times faster than rate of solution of
a supercritical fluid into groundwater. Also, a caprock layer (a sealing
layer or an impermeable layer) often exists in places like an oil field.
Even where there is no caprock layer (a sealing layer or an impermeable
layer), the fine bubbles of carbon dioxide go into gaps between the soil
particles, and become stabilized. The weight of carbon dioxide under 1
atm and at 0° C. is 1.98 kg/m3. So, for example, if 50 kg of
carbon dioxide is to be dissolved in 1 m3 of water, it is possible
to stabilize about 25 m3 of carbon dioxide in 1 m3 of the
groundwater.

[0017]The invention described has the following effect. A cation-forming
material (e.g., coal ash, calcium hydroxide, blast-furnace slag, or
liquid glass) is dissolved in the injection water. The injection water is
then injected into the top portion of the aquifer, at a place that is
above the place where the gas-liquid mixture has been injected. Thus, the
fine bubbles injected into the deep aquifer react with cations, and, as a
result, a barrier of carbonate compound is created. Therefore, upward
diffusion of carbon dioxide is prevented. In other words, an artificial
sealing layer is formed.

[0018]The present invention's system described for storing carbon dioxide
underground has the following effect. Carbon dioxide is turned into fine
bubbles so as to be dissolved in groundwater that has been pumped up from
a deep aquifer. Therefore, it is possible to dissolve a larger amount of
carbon dioxide--an amount larger than when using a conventional
method--into the injection water. In addition, the carbon dioxide that
does not become dissolved is mixed with the injection water so as to form
a gas-liquid mixture that is fed into the deep aquifer. The fine bubbles
go into the gaps between the soil particles, react with minerals in the
soil particles, and change into, for example, carbonate minerals. The
carbon dioxide is thus stabilized.

[0019]In the invention described, a double pipe is used for the injection
well, and therefore it is possible to simultaneously feed both injection
water and carbon dioxide to the bottom of the injection well. This leads
to instantaneous production of a gas-liquid mixture in the injection
well, and there is no need for a special mixing device aboveground.

[0020]The invention described uses a nozzle in which a carbon-dioxide
spray pipe is connected with an injection-water spray pipe. As a result,
carbon dioxide bubbles can be produced efficiently.

[0021]The invention described utilizes an inner-pipe raising/lowering
device that raises and lowers the inner pipe so that it can be inserted
into, removed from, and reinserted into the outer pipe, and a
cation-forming-material dissolving device. Therefore, a cation layer of,
for example, calcium hydroxide, can be formed above the gas-liquid
mixture that has been injected. Accordingly, even if the fine bubbles
injected into the deep aquifer go upward, the upward diffusion path of
carbon dioxide is blocked by the carbonate compound barrier that has been
created due to the reaction between the fine bubbles and the cations. In
other words, an artificial sealing layer is formed. Incidentally, after
the inner pipe and the nozzle are pulled up, a new slit is opened at an
appropriate place in the intermediate part of the outer pipe.

[0022]Still other objects and advantages of the present invention will
become readily apparent to those skilled in the art from the following
detailed description, wherein the preferred embodiments of the invention
are shown and described, simply by way of illustration of the best mode
contemplated of carrying out the invention. As will be realized, the
invention is capable of other and different embodiments, and its several
details are capable of modifications in various obvious aspects, all
without departing from the invention. Accordingly, the drawings and
description thereof are to be regarded as illustrative in nature, and not
as restrictive.

BRIEF EXPLANATION OF THE DRAWINGS

[0023]The present invention is illustrated by way of example, and not by
limitation, in the figures of the accompanying drawings, wherein elements
having the same reference numeral designations represent like elements
throughout and wherein:

[0084]The present invention's method for storing carbon dioxide
underground, and system for treating carbon dioxide will now be described
with reference to the drawings. FIG. 7 shows the general structure of
underground layers. The deep aquifer 50 is a water-permeable layer that
includes fine sand layers and that is saturated with salt water not
suitable for use as a water resource. Here, a depth of about 1000 m
underground is regarded as a deep layer. Also, there is an impermeable
layer 51 above the deep aquifer 50. Storage of carbon dioxide in the deep
aquifer can be expressed by the following reaction formulas. The
dissolution of carbon dioxide in water is expressed by
CO2═H2O═H2CO3. The ionization of this
dissolved carbon dioxide is expressed by
H2CO3═H++HCO3.sup.-. The reaction of this ionized
dissolved carbon dioxide with soil particles is expressed by, for
example, CaSiO3+HCO3.sup.-═CaCO3+SiO2+H2O.
CaCO3 is a carbonate compound, which means that the carbon dioxide
has been stabilized.

Embodiment 1

[0085]FIG. 1 shows the constitution of the present invention's system for
storing carbon dioxide underground.

[0086]The carbon-dioxide treating system 100 includes [0087]a pumping
well 20 that reaches a deep aquifer 50, [0088]a pump 1 that pumps up
groundwater 53 from the pumping well 20, [0089]an injection well 21 that
reaches the deep aquifer 50, [0090]a liquid injection device 2 that feeds
pumped-up groundwater 53--as injection water 54--into the injection well
21, [0091]a gas injection device 4 that feeds into the injection well 21
carbon dioxide 55 that has been separated and recovered from exhaust gas
from an outside plant facility 3, and [0092]a nozzle 5 that changes the
carbon dioxide 55 into fine bubbles inside the injection well 21.

[0093]The carbon dioxide 55 is changed into fine bubbles by the nozzle 5,
and the fine bubbles are then dissolved in the injection water 54. A
gas-liquid mixture 56 of carbon dioxide 55 and injection water 54 is
injected into the deep aquifer 50. The plant facility 3 includes a
thermal power plant and a garbage incinerator facility. Although there
are multiple layers from the soil surface 58 to the deep aquifer 50 at,
for example, a depth of 1000 m underground, only one layer, that of the
deep aquifer 50, is shown here.

[0094]A double pipe 8a that includes an inner pipe 6a and an outer pipe 7a
is installed in the pumping well 20. The pump 1 includes a pumping pump
9, a jet suction part 10, a water storage tank 11, a water feeding pump
12, and the double pipe 8a. Pressurized water 57 is fed to the inner pipe
6a by the pumping pump 9 in order to pump up the groundwater 53, which in
turn is pumped up by the jet suction part 10 so as to be stored in the
water storage tank 11. The jet suction part 10 increases the rate of flow
of the pressurized water 57 so as to generate negative pressure in order
to suck in the groundwater 53. The groundwater that is stored in the
water storage tank 11 can be circulated so as to be used as the water to
be put into the pumping pump 9. The water storage tank 11 can be equipped
with a useful-gas extracting device 29, which recovers methane and other
gases contained in the underwater 53.

[0095]The liquid injection device 2 includes [0096]a water injection
tank 13, [0097]a water injection pump 14 for feeding the injection water
54 into the injection well 21, [0098]a filter 15 for removing impurities
from the groundwater, and [0099]a cation-forming-material dissolving
device 30.

[0100]The distance between the pumping well 20 and the injection well 21
typically is from 500 m to 1 km, and the water storage tank 11 is
connected with the water injection tank 13 by a pipeline. The
cation-forming-material dissolving device 30 injects a cation-forming
material--for example, coal ash, blast-furnace slag, calcium hydroxide,
water glass, and the like--into the water injection tank 13. The carbon
dioxide reacts with the cation-forming material over time and becomes
stabilized as a carbonate compound. If the impermeable layer at the top
of the deep aquifer 50 is fragile and needs to be reinforced, urgent
reinforcement can be done based on results obtained through a monitoring
well. In other words, it is possible to achieve stabilized storage of
carbon dioxide in the deep aquifer for a long period of time.

[0112]As shown in FIG. 1, flow-control valves 25a, 25b, pressure control
valves 26a, 26b, 26c, a flow meter 27, and pressure meters 28a, 28b are
mounted to the liquid injection device 2 and to the gas injection device
4. When the plant facility 3 is near the injection well 21, the
feeding-side carbon-dioxide storage tank 23 can be connected to the
receiving-side carbon-dioxide storage tank 24 by a pipeline. When the
plant facility is away from the injection well, carbon dioxide can be
transported by a tanker. In the carbon-dioxide separating-and-recovering
device 17, the carbon dioxide can be condensed to a concentration of 90%
or higher, using a chemical-absorption technique.

[0113]The injection well 21 is provided with a double pipe 8b that
includes an inner pipe 6b and an outer pipe 7b. The carbon dioxide 55 is
fed to the inner pipe 6b, and the injection water 54 is fed into between
said outer pipe 7b and said inner pipe 6b. Thus, the double pipe 8b is
commonly used with the liquid injection device 2 and the gas injection
device 4. It also is possible for the injection well 21 to not be
provided with a double pipe 8b. However, if a double pipe 8b is used, a
gas-liquid mixture 56 can be produced at a deep part of the deep aquifer
50. A nozzle 5 is installed at the bottom end of the inner pipe 6b. The
carbon dioxide 55 is changed into bubbles that are emitted from the
nozzle 5 into the injection water 54 so as to produce the gas-liquid
mixture 56. Due to the injection pressure of the pumps, the gas-liquid
mixture 56 is diffused in the deep aquifer 50 from a slit formed at the
bottom of the outer pipe 7b.

[0114]The gas-liquid mixture 56 can have higher permeability than that
possible for only a liquid containing no gas. When the gas is in the form
of fine bubbles, it is difficult for the fine bubbles to solidify, and
therefore, the gas-liquid mixture 56 can be diffused well in the deep
aquifer 50. Some of the fine bubbles in this process burst, while the
other fine bubbles enter the gaps between sand particles and become
stabilized. When carbon dioxide is injected in the form of a
supercritical fluid, a solid (plume) is formed, but in this case plume
formation does not occur.

[0115]FIG. 2 is a cross-sectional view of the double pipe of the pumping
well. The jet suction part 10 is shaped into an inverted funnel so as to
increase the rate of flow of the pressurized water from the inner pipe
6a. The inside of the inverted funnel shape is under negative pressure,
and therefore, the jet suction part 10 can suck in the groundwater 53.
The sucked-in groundwater 53 goes up between the inner pipe 6a and the
outer pipe 7a. The pumping pump 9 must be capable of pumping up the
groundwater 53 to a height of 1000 m when the depth of the pumping well
20 is 1000 m.

[0116]FIG. 3 is a cross-sectional view that shows the double pipe of the
injection well and related elements of this embodiment. An inner-pipe
raising/lowering device 31 is mounted to the aboveground part of the
double pipe 8b.

[0117]The inner-pipe raising/lowering device 31 includes [0118]a
suspension fixture 40 that is mounted to the upper end of the inner pipe
6b, [0119]a pulley 39 that extends from the pulley block at the top of
the tower 36, [0120]a winch (hoisting machine) 37 that is installed on
the ground, and [0121]a winding-and-rewinding wire rope 38.

[0122]The inner pipe 6b and the nozzle 5 that is mounted at the bottom of
the inner pipe 6b are raised or lowered by the inner-pipe
raising/lowering device, and therefore, the gas-liquid mixture 56 can be
injected not only into the bottom of the injection well but also at the
top of the injection well. Also, when the fluid is injected at the top, a
new injection slit needs to be provided to the outer pipe 7b. So, the
inner pipe 6b and the nozzle 5 are pulled up above the ground, and the
outer pipe 7b is bored, using an explosive, so as to form the new slit.
After the inner pipe 6b and the nozzle 5 are lowered again to be set in
the position shown in FIG. 3, the fluid is injected.

[0123]To produce carbon dioxide bubbles in the injection water 54 using
the nozzle 5, the same method as that for discharging air in the form of
fine air bubbles into water can be applied. This can be an injector
method, a swirling-flow method, or a cavitation method. Here, an injector
method having a simple structure is adopted, and the nozzle is
constituted so as to be suitable for the double pipe. The outside
diameter of the nozzle 5 equals the inside diameter of the outer pipe 7b,
and the nozzle 5 is mounted to the bottom of the inner pipe 6b. An
inclined injection-water spray pipe 32, one end of which is opened
between the outer pipe 7b and the inner pipe 6b and the other end of
which is opened at the bottoms of the outer pipe 7b and the inner pipe
6b, is installed inside the nozzle 5. A carbon-dioxide spray pipe 33, one
end of which is opened to the inner pipe 6b and the other end of which is
connected with the intermediate portion of the injection-water spray pipe
32, is also installed. Plural sets of injection-water spray pipes 32 and
carbon-dioxide spray pipes 33 are provided.

[0124]Because the flow path of the injection-water spray pipe 32 is
narrow, the rate of flow of the injection water 54 is high, and the
portion of the inside of the injection-water spray pipe 32 that is
connected with the carbon-dioxide spray pipe 33 that is connected with
the injection-water spray pipe 32 is under negative pressure, and thus
the carbon dioxide 55 is drawn into the injection-water spray pipe 32 in
the form of bubbles 34. The cross-sectional area at the bottom of the
outer pipe 7b is larger than that of the portion of the outer pipe 7b at
which the inner pipe 6 is situated, and therefore the pressure of the
injection water 54 inside the inner pipe is significantly less than the
pressure outside the inner pipe. Thus, the generation of fine bubbles by
cavitation is promoted. Here, the diameter of the fine bubbles is from
about 0.01 mm to several mm. A device for generating so-called
microbubbles having a diameter of 50 μm or less can be used.

[0125]The slit 35 at the bottom of the injection well 21 is at L0. If the
resistive pressure of the deep aquifer at that point is P0, the pressure
of the non-bubble injection water is P0+Pα. Pα is about 1.0
MPa at maximum. In the case of the gas-liquid mixture 56, the water
pressure is reduced to (Pβ) due to the bubbles 34, so the fluid must
be pressurized as much as that reduced pressure (Pβ). Therefore, the
pressure of the injection water 54 must be P0+Pα+Pβ. From this
pressure, the emission pressure of the water injection pump 14 is
determined. Even if the carbon dioxide 55 is not pressurized, the carbon
dioxide 55 is drawn toward the injection-water spray pipe 43 by the
nozzle 5. If it is desired to increase the mixing volume of the carbon
dioxide 55, the carbon dioxide 55 can be slightly pressurized. As
described above, this system does not require a high
temperature-and-high-pressure facility for turning carbon dioxide into a
supercritical fluid.

[0126]FIG. 4 shows the arrangement of the pumping well and the injection
well. The arrangement and the number of injection wells 21 for carbon
dioxide are determined separately for each project according to the total
amount of carbon dioxide to be stored, the injection rate, the volume of
the objective deep aquifer, the permeability of the rock, and so on. FIG.
4 shows that carbon dioxide is stored at two periods of time. In the
first storage period, injection wells 21a, 21b are used, and pumping
wells 20a, 20b, 20c, 20d, 20e, 20h, 20f, 20g are used so as to surround
the injection wells. In the second storage period, in view of the
variation in soil permeability, injection wells 21c, 21d are used, and
the pumping wells 20b, 20i, 20c, 20e, 20h, 20f, 20g are used so as to
surround the injection wells. The pumping well is also used as a well for
monitoring storage status. It is necessary that the suction pressure of
the pumping well 20 pumping up from the deep aquifer be balanced with the
injection pressure of the injection well 21 that is injecting carbon
dioxide 55 into the deep aquifer.

[0127]FIG. 5 is a cross-sectional view along the line A-A of FIG. 4. The
non-storage layer 59 under the soil surface 58 is a layer not suitable
for storing carbon dioxide. Also, if there are multiple deep aquifers,
carbon dioxide is first stored in the deepest deep aquifer 50a.
Thereafter, the cation-forming material is injected at the top of that
deep aquifer 50a, carbon dioxide is stored in the deep aquifer 50b above
that one, and then the cation-forming material is injected into the top
of the deep aquifer 50b. If the impermeable layer 51a is thick and rigid,
injection of the cation-forming material at the top of the deep aquifer
50a can be omitted. After completion of all injecting operations, the
pumping wells and the injection wells are left to be used as monitoring
wells.

[0128]FIG. 6 is a flow chart showing the procedure for storing carbon
dioxide underground. Each of the numbers 60-64 denotes a treatment step.

[0129]Although the present invention relates to underground storage of
carbon dioxide, it can also be applied to underground storage of other
global-warming gases.

[0130]It will be readily seen by one of ordinary skill in the art that the
present invention fulfils all of the objects set forth above. After
reading the foregoing specification, one of ordinary skill in the art
will be able to affect various changes, substitutions of equivalents and
various aspects of the invention as broadly disclosed herein. It is
therefore intended that the protection granted hereon be limited only be
definition contained in the appended claims and equivalents thereof.